Type 2 diabetes (T2D) is a pandemic disease that shows little sign of decline.1 Rates of obesity are increasing worldwide.2 It is now clear that obesity is associated with an increased risk of developing insulin resistance and T2D.3 A novel peptide was recently identified by Boström et al.4 and has been named ‘irisin’ by the researchers after the Greek messenger goddess Iris. Irisin acts on the cells of white adipose tissue. Interestingly, concentrations of irisin increase significantly after endurance exercise training in both mice and humans. Moreover, irisin levels in the blood are correlated with irisin mRNA levels in muscle tissue.4 Irisin increases total energy expenditure and, in certain animal models, prolongs life expectancy, reduces body weight, and mitigates diet-induced insulin resistance, thus reducing obesity and insulin resistance.4
It has been postulated that irisin could serve as an injectable treatment for metabolic disease and other disorders for which physical exercise may lead to improvements, such as obesity and T2D.4 Several compounds that may act to improve such disorders have been discovered and evaluated. A few years ago, exercise-mimetic drugs such as 5′-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) and GW1516 (a modulator of peroxisome proliferator-activated receptor δ) were suggested as potential treatments for obesity.5 This suggestion led to questionable announcements about these drugs in the media, such as ‘exercise in a pill’.6 However, the side effects of AICAR are contentious (see http://www.outsideonline.com/outdoor-adventure/natural-intelligence/faster--higher--squeakier-.html?page=all, accessed 10 February 2012) and a specific disease application for this compound has not been identified so far. Because the US Food and Drug Administration (FDA) will not approve any drug without proven clinical application, such treatments remain at the development stage. Nevertheless, it is imperative to develop pioneering and suitable formulations to guarantee that patients with conditions such as obesity have access to appropriate medication. Although optimism should be guarded, the identification of irisin opens new possibilities because it is an endogenous hormone that can be cloned easily using recombinant DNA technology. Recombinant human proteins (e.g. insulin, growth hormone, erythropoietin) are used widely in modern therapeutics. Although much work is still needed, the application of irisin may prove beneficial not only in the treatment of obesity and diabetes, but also for a wide range of pathological conditions that are characterized by a variable imbalance of energy demand and expenditure.